The easy way for entities or negative Spirits to get hold of you is when your energy is low and your psychic boundaries have been weakened.
They like to hang around Hospitals, Prisons and Nightclubs.
They may for example attach when you are very drunk or high on drugs, after an operation, or when you have been ill with either a physical or mental illness.
We are not talking about Angels or Spirit guides the accompanying, supportive and good energies; not bound to our dimension or earth plane.
The troublemakers of Earth bound spirits are very different they are ill-natured, malicious, spiteful or simple evil.